Paper containing a polymer mixture of polysulfonium resin and polycarboxylate resin



United States Patent 3,146,157 PAPER CONTAINING A POLYMER MIXTURE OF POLYSULFONIUM RESIN AND POLYCARBOX- YLATE RESIN Robert W. Morgan, Saginaw, and Melvin J. Hatch, Midland, Mich, assignors to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Jan. 8, 1962, Ser. No. 165,001 9 Claims. (Cl. 162-164) The present invention concerns improved webs of cellulose fibers and a method for their manufacture. Particularly, the invention involves treating wet felted, cellulosic webs, such as paper, with a combination of polymeric agents to increase their strength characteristics, especially wet strengths.

The art teaches incorporating various polymeric agents into cellulose fiber webs in order to improve their wet or dry strengths. It would be desirable to provide a novel treatment for cellulosic webs whereby simultaneous improvement of both Wet and dry strength properties of the Webs is achieved. Further, it would be most advantageous to provide substantial increases in wet strength of wet felted cellulosic webs solely with water-soluble polymeric agents, said agents being effective under widely varying pH conditions such as may occur with different chemicallyproduced cellulosic pulps. Attractive features of any such process would be the ease with which it could be carried out and the uniformity of polymer treatment levels in the resulting cellulosic Webs.

In accordance with this invention, an improved web of cellulosic fibers is obtained by incorporating therein sequentially, in any order or as a mixture, a water-soluble polymeric polysulfonium resin and a water-soluble polymeric polycarboxylate resin. Said polymeric additaments are employed in amounts such that the number of carboxylate moieties in the system is from about 0.1 to 1.5 times the number of the sulfonium moieties present.

For good results, the total amount of the combination of polymeric agents incorporated into the cellulosic web, i.e., the amount of the agents which is retained in the fibrous web, is from about 0.05 to about 3 percent by weight based on the dry fibers.

After incorporating said polymeric agents into the cellulosic fiber, it is desirable to condition the web by heating it at an elevated temperature for a short period of time. Usually this is accomplished by subjecting the treated web to a temperature of at least 40 up to as much as 170 C., preferably a temperature within the range from about 80 to about 120 C., for a period of "ice 7 screen. While it is most desirable to add the polymeric time ranging anywhere from about as little as 0.5 second to as much as 5 or 10 minutes depending on the temperature employed. Though an equivalent conditioning effect can be achieved by extended aging at room temperature, the aforementioned thermal treatment accelerates the desired strength improvements.

Most often, the invention is utilized in paper-making processes wherein the cellulose fiber web is formed by wet I ing the polymeric agents to the cellulosic pulp prior to the web-forming step. In such instances, the polymeric additaments can be added to the aqueous fiber dispersion sequentially in any order or as a single premixed composition.

agents to the pulp at a point in the process subsequent to any severe mechanical working of the pulp, such as may occur in the refiner, the point of such addition is not critical. The important consideration is the achievement of suflicient mixing of the additives with the pulp to provide a uniform dispersion thereof prior to the web-forming stage.

While it is conventional practice to utilize fiber pulps or slurries containing from about 0.1 to about 5 percent by weight dry fiber, the invention can be carried out even when substantially greater fiber concentrations are utilized.

For the treatment to be effective when carried out in the above manner, the pH of the fiber slurry can be anywherein the range from about 3 up to about 10. Usually, it is within the range from about 7 to 8.

The total amount of the combination of polymeric agents added to the cellulosic fiber slurry can vary from as little as 0.1 up to as much as 3 percent based on the dry weight of the fibers in the slurry. Usually, excellent results are achieved when the agents are employed in amounts from about 0.5 up to 1.5 percent based on the weight of the fibers is utilized.

The polymeric agents can be added to the cellulosic fiber stock in the form of solid compositions or aqueous solutions. To optimize the desired results, it is best to add them in the form of dilute aqueous solutions con taining from about 0.05 to about 10 weight percent polymer solids.

After adding the polymeric additaments to the cellulose fiber slurry in the specified relative proportions, the treated and suitable refined aqueous fiber slurry is passed onto any suitable sheeting equipment whereupon the fibrous suspended solids are felted from the aqueous dispersing medium in the form of a web-like sheet. Usually, these operations are continuous in nature and may be accomplished with such machines as the Fourdrinier paper machine and the like. The wet felted web may then be subjected to one or more finishing operations such as sizing or calendering. Ultimately, the treated cellulosic web is dried. Preferably such drying is done at a temperature high enough and for a period of time sufficient to accomplish conditioning of the treated prod- -uct as described hereinbefore.

Polymeric polysulfoniums useful in the invention are resinous, water-soluble polymers characterized as polyalkane backbone polymers having chemically integral therewith a plurality of sulfonium moieties, represented by the following general formula:

wherein R is selected from the group consisting of hydrogen, halogens and alkyls having up to 6 carbon atoms, Y is a divalent, sulfur-containing, organic radical having its valences on the sulfur atom, said radical being derived from acyclic and alicyclic organic sulfides having from 2 up to 12 carbon atoms, X is a counter anion and n is an integer from 1 to 4.

Water-soluble, as employed herein, means dispersible in water to provide a visually homogeneous and transparent solution infinitely dilutable with water.

The counter anions include such organic and inorganic anions as chloride, bromide, fluoride, iodide, sulfate, nitrate, bicarbonate, carbonate, acetate, propionate, benzoate and the like. Other anions preferred for their unexpected activity include dihydrogenphosphate, phthalate, succinate, oxalate and maleate. Polysulfoniums with anions of the latter class provide wet strengths up to as much as, or more than, 2 times that achieved with the aforementioned inorganic anions.

More particularly, Y corresponds to the following formula:

wherein R and R separately represent monovalent radicals such as, for example, alkyls, haloalkyls, hydroxyalkyls, carboxyalkyls, acyloxyalkyls, carboalkoxyalkyls, carbamoylalkyls, alkylcarbamoylalkyls, alkylamidoalkyls and (C,,H ,,Z) C H radicals wherein Z is selected from the group consisting of oxygen and sulfur, a is an integer from 2 to 4, b is at least 1, said monovalent radicals having from 1 up to 11 carbon atoms. Taken together, R R and S represent an alicyclic, saturated organic sulfide radical having from 4 to 6 ring carbon atoms which may contain such substituents as halogen, alkyl, amino, hydroxyl and the like groups.

Normally, the above-described sulfonium moiety will have a halide counter anion such as the chloride ion. If desired, however, the halide form of the sulfonium group can be converted in a conventional manner to any one of the common anionic forms such as those mentioned above, by passing an aqueous solution of the water-soluble polymeric polysulfonium through an anion exchange in the proper salt form.

The polymeric polysulfonium additives of the invention can be prepared as homor copolymers of arvinyl aralkyl sulfonium monomer precursors to the aforementioned sulfonium moiety. They also may be prepared as copolymers of such monomers with other monoethylenically unsaturated monomers wherein the pro portion of the sulfonium moiety present in the finished polymer is at least about 2 percent of the reoccurring moieties and the resulting polymer is water soluble. Depending upon whether the comonomers are hydrophilic or hydrophobic, the minimum proportion of the sulfonium monomer required to maintain water solubility will vary considerably. In any event, a minimum proportion of about 65 percent by weight of the sulfonium monomer will usually insure water solubility of the resulting copolymer. Comonomers that can be employed include styrene, vinyltoluene, a-methylstyrene, vinylpyridine, ethyl acrylate, ethyl methacrylate, 2- aminoethyl methacrylate, N-methyl-Z-aminoethyl methacrylate, acrylamide, methacrylamide and the like.

Homopolymerization of the ar-vinyl aralkyl sulfonium monomers or copolymerization of at least one such arvinyl aralkyl sulfonium monomer with one or more other monoethylenically unsaturated monomers can be carried out by any convenient method such as those conventionally employed to polymerize the free radical catalyzed vinyl systems. For this purpose, mass, emulsion or solution polymerization techniques employed in conjunction with such polymerization-initiating means as actinic light, ultraviolet radiation, gamma radiation, azo catalysts and peroxides are adaptable with such modifications as are necessary to accommodate the particular properties and reaction characteristics of the monomeric reactants to provide efiective means of preparation.

Water-soluble, polymeric polysulfoniums can also be prepared by reacting a suitable organic sulfide with a linear polymer containing in chemically combined form at least an effective proportion, e.g., at least about 2 percent, when the polymer is otherwise essentially watersoluble, or at least about 65 percent, when the polymer is otherwise essentially hydrophobic, of the combined monomers of an ar-vinyl aralkyl halide. Preferably, such a method of preparation is limited to reactions with organic sulfides in which at least one of the organic substituents on the sulfur atom contains no more than 2 carbon atoms. For instance, a homopolymer of vinylbenzyl chloride or a chloromethyl-ated polystyrene having chloromethyl groups on at least about 65 percent of the reoccurring aromatic moieties is contacted with a stoichiometric quantity of an organic sulfide such as dimethyl sulfide in a mass reaction at a temperature from about 20 to about 70 C. to provide a polymeric polysulfonium chloride.

Another class of polymeric polysulfonium compositions are high molecular weight, lightly cross-linked, watersoluble polymeric polysulfonium microgels. These polymers can be prepared in a manner similar to that employed for the preparation of the aforementioned linear polymers except that a small quantity of a cross-linking agent such as, for example, divinylbenzene, is employed in the polymerization reaction. Illustratively, a small amount of a divinyl cross-linking agent is copolymerized with an alkenyl aromatic monomer substituted with either a sulfonium halide group, in which instance a cross linked polymeric polysulfonium halide is directly prepared, or a haloalkyl group, in which instance a crosslinked, haloalkyl substituted polymer is prepared, which can be subsequently converted to a polysulfonium halide by means of a mass reaction with a suitable organic sulfide.

Cross-linking agents suitable for the above purpose include diolefins such as divinylbenzene, divinyl ether of ethylene glycol, ethylene glycol diacrylate, ethylene glycol dimethacrylate, glycerol trimethacrylate, diallyl itaconate, diallyl maleate, diallyl fumarate, diisopropenyldiphenyl and the like.

To provide lightly cross-linked and high molecular weight, but yet water-soluble, polymers, it is necessary to employ at least about 0.01 percent up to an upper limit of about 1 percent by Weight of the total polymer of the diolefinic cross-linking agent. Generally, it is pre ferred to employ about 0.05 percent by weight of the cross-linking agent.

The polymeric polycarboxylate agents employed in the present invention are high molecular weight synthetic organic polymers corresponding to the vinyl polymerization products of monoethylenically unsaturated monomers bearing a carboxylate group or copolymers of such a monomer with other suitable ethylenically unsaturated monomers capable of undergoing vinyl polymerization. It is essential that such copolymers contain sufiicient carboxylate-bearing monomers or sufiicient carboxylated monomers with other monomers having water-solubilizing substitutent groups to render the copolymer water soluble. Also, it is essential that at least about 4 percent of the monomer moieties combined in the finished polymer should bear a carboxylate group. Desirably, about 20 percent of the combined monomer moieties should hear such substituents.

Carboxylate, as used herein, refers to the protonated forms thereof, i.e., the carboxylic form, as well as the conventional salt forms including, for example, alkali metal, alkaline earth metal, ammonium, substituted ammonium and methyl-, dimethyland trimethylamine carboxylates.

By high molecular weight, as applied to the above polymeric polycarboxylate agents, is meant a weight average molecular weight of at least about 25,000. Preferably, however, higher molecular weight polymers are used since their effectiveness in the present invention improves with increasing molecular weights.

or methacrylamide or as the copolymerization products of such monomers with other suitable monomers including, for example, acrylonitrile, methacrylonitrile, lower alkyl esters of the acrylic acids, vinyl alkyl ethers and the like monoethylenically unsaturated compounds. During the polymerization reaction or thereafter with appropriate treatments, the carboxamide-containing polymer is partially hydrolyzed to provide a desired number of anionic carboxylic groups. Usually, such copolymers contain in chemically combined form at least about 85 mole percent of the acrylamide or methacrylamide and not more than about mole percent of the other monomers. Acrylic polymer products appear to be equivalent whether the carboxylate content results from copolymerization of acrylamide with acrylic acid or a salt thereof or from hydrolysis of carboxamide groups subsequent to polymerization.

Still another variety of polymeric polycarboxylates suitable for use in accordance with the invention is that of the high molecular weight, water-soluble copolymers of styrene and maleic anhydride and the like carboxylic monomers. Such copolymers are generally employed in the form of their alkali metal salts, preferably the sodium salt, although the acid form obtained by hydrolsis of the anhydride rings may also be employed.

The following examples illustrate the invention but should not be construed as limitations thereof.

EXAMPLE 1 Air dry, unbleached hardwood soda pulp was beaten to a desired Canadian standard freeness of about 400 milliliters in a Valley beater. A sufiicient amount of the beaten pulp to provide 5 grams of dry fibers was removed from the beater and dispersed in suificient additional water along with a desired amount of the polymeric agents of the invention to provide a total composition volume of 2 liters. The polymeric additaments were added to the fiber slurry in the form of dilute aqueous solutions containing about one percent by weight polymer solids con sisting of a mixture, as hereinafter specified, of the polycarboxylate and polysulfonium agents used. Enough of the polymer solution was used to provide about 0.5 percent by weight polymer solids based on the dry fibers. The pH of the resulting fiber dispersion-polymer solution was usually about 6 unless otherwise specially adjusted.

Next, a hand sheet was prepared from the treated fiber slurry in accordance with the procedure of TAPPI Standard T205m-53. The wet layed hand sheets were placed between a /2 inch thick felt pad and a polished metal plate. A thermocouple was placed between the wet fiber sheet and the lower felt pad and connected to a temperature recording device. Drying of the hand sheet was accomplished by slightly pressing the felt-Web-plate assembly in an Elmes Hydrolair laboratory hot press, the top platen of which was heated to 110 C. The drying operation was conducted for periods of time within the range from 2 to 6 minutes. The maximum temperature achieved during the drying period was recorded.

After drying, the hand sheet was conditioned at 70 F. and 65 percent relative humidity for at least 48 hours before being tested. The conditioned sheets were tested to determine their dry burst improvement and wet strength.

Dry burst improvement was determined according to TAPPI Standard T-403m-53 which defines the dry burst improvement as the dry burst strength of the tested hand sheet minus the dry burst strength of an untreated hand sheet divided by the dry burst strength of the untreated paper multiplied by 100, the burst strengths being corrected for basis weight. The wet burst strength of the hand sheet was determined by a similar technique except that the hand sheet was first soaked in deionized water for 24 hours. The wet strength of the hand sheet is the wet burst strength of the treated hand sheet divided by the dry burst strength of the same paper multiplied by 100, the burst strengths being corrected for basis weight.

The polymer treatment, curing conditions and strength properties of several hand sheets prepared according to the above-described procedure was reported below in Table 1.

Table 1 Cure conditions Strength properties Run Polymer treatment Drying Drying Dry Wet temp., time burst strength 0. (minutes) improve- (percent) ment (percent) None (Control). 107 6 1 A1. 106 2 11 1 100% A1 108 6 16 1 100% S1 103 2 22 12 67% S1+33% A1... 105 2 49 19 80% S1+20% A1..- 105 l 2 44 1s 91% Sl+9% A1. 103 2 27 15 10 107 6 40 16 67% S|+33% A1. 108 6 61 21 80% S +20% A1 108 6 55 22 91% S1+9% A1.... 107- 6 48 19 102 1 13 10. 8 S +33% A2". 102 1 43 16. 5 80% S1+Q0% A2.-. 102 1 35 18.1 89% s,+11% A 7 102 1 24. 8 16.5

a A1 is a high molecular weight, partially hydrolyzed polyaerylarnide wherein at least about 25 percent of the available carboxamide groups are hydrolyzed to carboxylic groups. The polymer had a molecular weight above 1 million.

b S1 is poly bis(2-hydroxyethyl)ar-vinylbenzyl sulfonium chloride having a molecular weight of about 20,000.

0 A2 is a homopolymer of methacrylic acid having a molecular weight; of approximately 25,000.

d The fiber slurry used had an adjusted pH of 9.

Results comparable to those achieved in the foregoing example can be accomplished by substituting for the polymeric polysulfoniums employed therein, resinous polymers of bis(2-carboxyethy1) ar-vinylbenzyl sulfonium chloride, 2-hydroxyethyl methyl ar-vinylbenzyl sulfonium chloride, bis(2-carbamoylethyl) ar-vinylbenzyl sulfonium chloride or copolymers of at least about 65 percent by weight bis (Z-hydroxyethyl) ar-vinylbenzyl sulfonium chloride with a balance of one or more monomers such as styrene, vinyltoluene, ix-methylstyrene, ethyl methacrylate, Z-aminoethyl methacrylate or similar copolymers of Z-carbamoyl ethyl methyl ar-vinylbenzyl sulfonium acetate with Z-aminoethyl methacrylate, acrylamide and acrylonitrile.

In like manner, comparable results to those achieved in the example above are provided by substituting for the polymeric polycarboxylate used therein, resinous polymers of acrylic acid, vinylbenzoic acid or carboxymethyl acrylate. Other polymers that can be used are partially hydrolyzed polyacrylonitrile, partially hydrolyzed po1ymethylacrylate and the like polymers wherein the extent of hydrolysis is sufficient to impart water-solubility to the copolymer. Also operable are water-soluble copolymers of styrene and maleic acid.

What is claimed is:

1. A cellulose fiber web having incorporated therein from 0.05 to 3 percent based on the weight of the fibers of a polymer mixture comprising:

(A) a water-soluble polymeric polysulfonium resin characterized as a polyalkane having chemically integral therewith a plurality of at least about 2 percent of the reoccurring moieties of sulfonium moieties represented by the formula:

wherein R is selected from the group consisting of hydrogen, halogens and alkyls having up to 6 carbons, Y is a divalent, sulfur-containing organic radical having its valences on the sulfur atom, said radical being selected from the group consisting of acylic and alieyclic organic sulfides having from 2 to 12 carbons, X is a counter anion and n is an integer from 1 to 4, and

(B) a water-soluble polymeric polycarboxylate resin having a weight average molecular weight of at least about 25,000 wherein at least about 4 percent of the combined monomer moieties bear a earboxylate p, the relative amounts of the polymeric additaments used being such that the number of carboxylate moieties in the Web are from about 0.1 to 1.5 times the number of sulfonium moieties present.

2. An article as in claim 1 wherein the polymeric polysulfonium is poly bis(2-carboxyethyl) ar-vinylbenzyl sulfonium chloride.

3. An article as in claim 1 wherein the polymeric polysulfonium is poly bis(2-hydroxyethyl) ar-vinylbenzyl sulfonium chloride.

4. An article as in claim 1 wherein the polymeric polysulfonium is poly bis(2-carbamoylethyl) ar-vinylbenzyl sulfonium cholirde.

5. An article as in claim 1 wherein the polymeric poly sulfonium is poly 2-hydroxyethyl methyl ar-vinylbenzyl sulfonium chloride.

6. An article as in claim 1 wherein the polymeric polysulfonium is a copolymer of at least 65 percent by weight of bis(2-hydroxyethyl) ar-vinylbenzyl sulfonium chloride with a balance of at least one monomer selected from the group consisting of styrene and a-methylstyrene.

7. In a process for manufacturing paper wherein a cellulose fiber slurry is wet layed to form a fibrous web, the improvement which consists in mixing with said slurry from 0.05 to 3 percent, based on the weight of the fibers, of a polymer mixture comprising:

(A) a water-soluble polymeric polysulfonium resin char- E; acterized as a polyalkane having chemically integral therewith a plurality of at least about 2 percent of the reoccurring moieties of sulfonium moieties represented by the formula:

wherein R is selected from the group consisting of hydrogen, halogens and alkyls having up to 6 carbons, Y is a divalent, sulfur-containing organic radical having its valences on the sulfur atom, said radical being selected from the group consisting of acyclic and alicyclic organic sulfides having from 2 to 12 carbons, X is a counter anion and n is an integer from 1 to 4, and

(B) a water-soluble polymeric polycarboxylate resin having a weight average molecular weight of at least about 25,000 wherein at least about 4 percent of the combined monomer moieties bear a carboxlate group, the relative amounts of the polymeric additaments used being such that the number of carboxylate moieties in the web are from 0.1 to 1.5 times the number of sulfonium moieties present.

8. A process as in claim 7 wherein the pH of the cellulose fiber slurry is within the range from about 3 to about 10 and the total amount of the polymers dissolved in the slurry is from about 0.1 up to about 3 percent by weight of the fibers on a dry basis.

9. A process as in claim 7 wherein the combination of polymeric agents incorporated into the cellulose fiber slurry is in the form of a dilute aqueous solution containing from about 0.05 to about 10 weight percent polymer solids.

References Cited in the file of this patent UNITED STATES PATENTS 2,768,990 Dejong Oct. 30, 1956 2,895,925 Hwa July 21, 1959 2,923,700 Price et a1 Feb. 2, 1960 2,989,520 Rutenberg et a1 June 20, 1961 3,060,156 Rassweiler et al Oct. 23, 1962 FOREIGN PATENTS 1,031,228 France Mar. 18, 1953 

1. A CELLULOSE FIBER WEB HAVING INCORPORATED THEREIN FROM 0.05 TO 3 PERCENT BASED ON THE WEIGHT OF THE FIBERS OF A POLYMER MIXTURE COMPRISING: (A) A WATER-SOLUBLE POLYMERIC POLYSULFONIUM RESIN CHARACTERIZED AS A POLYALKANE HAVING CHEMICALLY INTEGRAL THEREWITH A PLURALITY OF AT LEAST ABOUT 2 PERCENT OF THE REOCCURRING MOIETIES OF SULFONIUM MOIETIES REPRESENTED BY THE FORMULA: 